My specific point was to caution against using general assumptions. The mass balance for solids is clear, and while assumptions such as that may be true with biosolids the OP did individually mention COD and BOD separately as load for the plant, and not simply biosolids as the sole source of COD loading. "Food processing" can also produce wastes with purely chemical conversion which must be satisfied before any of the bacteria present can thrive, not unlike ammonia/nitrogen load in a typical municipal plant where nitrogenous bacteria will be consuming almost all available oxygen before carbonaceous BOD is consumed. Furans, mercury, dioxins, chelated surfactants, and other high strength load can stream from "food processing" operations in amounts which will kill a municipal treatment plant faster than a pharmaceutical waste stream, so understanding the load before accepting it might just be important.
As for the second suggestion, one cannot easily apply an anaerobic process with high VOCs like benzene, toluene, hexane, trichloroethylene, and some of the constituents in the waste stream from a chemical processing operation.
Again, the most practical resolution may be dependent upon the source(s) of waste which is why I asked, and why the OP should ask his potential contributor for analysis.